The relationship of chromatin structure and composition to gene regulation will be investigated in a differentiating cartilage system derived from the embryonic chick limb. Chromatin from progenitor and terminally differentiated cartilage cells will be fractionated using several different deoxyribonucleases. The nonhistone chromatin protein composition of the various fractions will be analyzed by two-dimensional SDS gel electrophoresis. The relation of each fraction to template active and inactive chromatin will be determined by assaying radioactivity in the various chromatin fractions prepared from chromatin that has been labelled in its active regions by nick-translation. These studies will also be performed on embryonic limb cells of talpid2 chicken embryos, which exhibit an abnormal cartilage differentiation and an altered cell-type specific nonhistone chromatin protein in limb bud mesenchyme.